During the assembly of semiconductor packages, semiconductor chips are often attached onto carriers, such as substrates or leadframes, for processing multiple semiconductor chips at the same time. After or during attachment, electrical connections are made between electrical pads on the chips to corresponding contacts or connection pads on the substrates or leadframes. This can be done by wire bonding, or the electrical pads can be directly attached onto the contacts on the substrates or leadframes. Thereafter, it is usually necessary to protect the chips and the electrical connections from the environment by encapsulating them in a molding compound, such as epoxy molding compound (“EMC”).
In a typical transfer molding process, the substrate or leadframe with the chips attached is placed into a molding system comprising two mold halves. One or more molding cavities are formed in one or both of the mold halves corresponding to the positions of the chips to be encapsulated. Molding compound is introduced into mold supply pots in the molding system, typically in pellet form. The mold supply pots are linked to the molding cavities through a system of runners and gates through which the molding compound is channeled before entering the cavities. A plunger is insertable into each pot under heat and pressure to crush the pellet and distribute molding compound under the pressure from the plunger through the system of runners and gates and into the molding cavities.
After the cavities have been filled, the molding compound is allowed to set. Besides molding compound that is filled into the cavities for encapsulation, excess molding compound is also created inside to the mold supply pot, and in the runners and gates.
FIG. 1 is a plan view of a molding surface of a lower mold 10 including leadframes 12 that have been encapsulated in the mold 10. Each leadframe 12 contains encapsulated packages 14 corresponding to positions of semiconductor chips that have been attached onto the leadframe 12. Excess molding material 15 is still attached to the encapsulated packages 14, and it can be conveniently referred to as the cull 16, runner 18 and gate 20 portions of the excess molding material 15. The encapsulated portion corresponding to the encapsulated packages 14 protects internal components (not shown) on the leadframe 12 and would be retained. The cull portion 16, runner portion 18 and gate portion 20 are not used and thus need to be removed and discarded before further processing of the leadframe 12.
Conventionally, an offloading arm will transfer the molded carriers from the lower mold 10 to a degating tool. Degating generally involves a process of clamping, punching or flipping the excess molding material to separate it from the electronic packages, and a special degating tool is used to undertake the process. The degated carrier is then transferred to yet another station for further processing as appropriate.
However, the aforesaid conventional degating approach has a number of shortcomings. A major disadvantage is that a separate station is required to accommodate the degating tool. This necessitates a higher cost involved in manufacturing a separate degating tool, and a larger resultant machine footprint takes up valuable floor space. Another disadvantage is that the degating tool has to be custom-made and can only be designed after the design of the mold tool is completed. Furthermore, the degating result, and therefore the quality of the encapsulated packages, cannot be known immediately after molding is performed, as it has to go through the degating station first. The need to have a separate station also means that time is allowed for the carrier to cool, which can be undesirable for some packages if warpage or thermal stress results after cooling.